Automatic Train Systems divide the railroad track into units called blocks. Wayside circuitry is capable of resolving vehicle location to within a block. To provide vehicle carried apparatus or a train operator with traffic information, other wayside circuitry transmits an indication of the distance between a vehicle and the immediately preceding vehicle. This information is coded so as to represent, at least, a speed limit. The speed limit is computed such that it is always possible for the following vehicle to stop within the unoccupied distance between vehicles. The actual speed is transmitted to the train operator via a speed probe connected to a speedometer.
If the actual speed exceeds the speed limit an overspeed condition is detected. When an overspeed condition is detected the governor may automatically impose a brake application; or signal the vehicle operator that he must impose a brake application. Unfortunately, the application of the brake may bring the vehicle under speed sooner than is actually required by the actual clear distance between vehicles, or the vehicle does not decelerate quickly enough.
To alleviate the problem of early braking or late deceleration, a profile speed calculated by a vehicle carried apparatus is utilized. See U.S. Pat. No. 4,495,578 (Sibley et al.), issued Jan. 22, 1985. The profile speed gradually decreases, say from a first or higher speed limit when the profile generation apparatus is initiated, to a lower or zero speed limit at the termination of the speed profile generation. That is, the profile speed is typically fed to the governor, along with the wayside generated speed limit, and safely allows the governor to control the vehicle to be at a speed below the higher of the two (speed profile or wayside generated) limits.
Conventionally available display units typically only display the actual speed of the vehicle. However, since the allowable speed (speed limit) and profile speed are extremely critical to proper vehicle operation, the present inventor found it necessary to develop a device capable of simultaneously displaying the relationship between actual, allowable, and profile speeds.
The present inventor undertook the development of a novel analog and digital display device which is capable of providing operational information, such as actual train speed, allowable train speed, profile speed, overspeed alarm, and many other parameters, simultaneously. The display format of the present invention allows for faster, more accurate interpretation of a greater number of operational parameters than conventional analog aspect displays. The design of the present invention is such that the information regarding the various speeds (i.e., actual, allowable and profile) can be displayed in both analog and digital formats.
The present invention also provides many additional advantages which shall become apparent as described below.